Astronomy Picture of the Day

Discover the cosmos! Each day we feature a different image or photograph of our fascinating universe, along with a brief explanation written by a professional astronomer.

September 4, 1995

Ganymede: Moonquake World
Credit: NASA, Voyager

Explanation: Ganymede probably undergoes frequent ground shaking events not unlike terrestrial earthquakes. Ganymede, the largest moon of Jupiter and the Solar System, has a thick outer coating of water ice. Passing Voyager spacecraft found a large number of cracks and grooves in the ice so it is thought that Ganymede, like the Earth, has large shifting surface masses called tectonic plates. Ganymede was discovered by Galileo and Marius in 1610, and is larger than the planets Mercury and Pluto. The NASA spacecraft Galileo is scheduled to arrive at Jupiter is December of 1995.

Tomorrow's picture: Europa: Ancient Water World

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